Perimeter Plate Nitrous system - Go, Baby, Go!

The ins and outs of installing a nitrous system

Don't tell me you haven't seen it. I know Corvette guys aren't supposed to like Mustangs, but if you're into car culture, you've definitely seen the part in Gone in 60 Seconds where Nicholas Cage flips the nitrous-arming switch on the '67 GT500 he's stealing, hits the little red button marked "go-baby-go," and loses the police helicopter that's closing in on him. Thanks in part to that scene, and the Fast and Furious franchise, nitrous oxide has steadily increased in popularity over the past several years.

Among the newer nitrous products is the adjustable Perimeter Plate system offered by Zex, which adds between 100 and 300 horsepower and is designed to overcome some of the weaknesses of traditional "plate"-style nitrous systems. Here, we'll look briefly at what nitrous is and does, and then take a more in-depth look at how to install the Zex kit on my red '72 small-block coupe, AKA "Scarlett."

Though still frequently considered a somewhat naughty addition to a car (note how many of the kits have "sneaky" or "cheater" in the name), using nitrous oxide to increase engine power is nothing new: As far back as World War II, the Nazi Luftwaffe used it to help airplane performance at high altitude. Not actually a fuel, nitrous oxide is composed of two parts nitrogen and one of oxygen; the latter element is released as the compound breaks down at high temperature. This aids the process of oxidizing fuel so that more can be burned, thus increasing the engine's power output.

The reason there's "no replacement for displacement" is that more room allows for more fuel to be burned. Nitrous essentially accomplishes the same thing in a smaller space, with little modification required to the engine. And unlike stroker kits, turbos, or superchargers, the extra power is only produced on demand, leaving fuel economy and general driveability unaffected.

Nitrous systems are generally divided into two types. In a "wet" system, the nitrous is mixed with additional fuel and sprayed into the intake tract. In a "dry" setup, the nitrous is sprayed by itself, and the fuel delivery system is calibrated or modified to deliver the additional fuel needed. One of the advantages of a wet system is that, since the fuel and nitrous are sprayed together, it's simpler than a dry system. This reduced complexity somewhat lessens the possibility that the nitrous will be sprayed in without the extra fuel.

Should the engine run lean (i.e., without sufficient fuel) while nitrous is being added, the result will be very high combustion temperatures, coupled with really good odds of engine damage. You've heard of melting pistons, and burning holes in them? Yep. That's why you'll need to be careful.

With a little caution, however, there's nothing to fear. Estimates vary, but assuming your engine is in good shape and unmodified, anything between 100 and 150 horsepower should be safe to add. Much over that, and you're going to need to beef some things up.

In this case, the engine we'll spray is a low-mileage ZZ2, a GM crate motor producing somewhere in the neighborhood of 345 hp and 400 lb-ft of torque. The kit Zex sent contained a Perimeter Plate for a standard Holley application (the company also has one that's Dominator compatible), fuel and nitrous solenoids, an assortment of jets, all the braided-steel line and electrical components required for installation, and a 10-pound nitrous bottle and mount. While mine came in Zex's trademark purple color, the kit is also available in a stealthy "Blackout" version. The bottle comes empty: Expect to pay around $4 per pound to fill it.

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There's nothing subtle about having a 10-pound purple bottle bolted into the back of your Corvette. Should you get pulled over for speeding, don't plan on getting any warnings.

1 Put the mounts on the bottle and place it where you want it to install it, being aware of any supports under the floor. Use masking tape under the mounts to mark the drill locations, since you'll have to remove the brackets to drill the holes. Drill from the top and use the included bolts and washers to mount the bracket. The carpet will tend to wrap around the drill bit, so you'll need to clean it every so often.

2 Route the braided line to the bottle by feeding it through the firewall, down behind the dash, and under the center console and e-brake housing. From there, you can either tuck it under the carpet and bring it over the top onto the back deck, or route it through a hole under the rear of the e-brake housing and up into the storage well that holds the jack.

3 Start the plate-mounting process by removing the air cleaner and everything attached to the carb, beginning where the cable meets the linkage on the outside. Next, unhook the return spring and loosen the clamp that holds the throttle cable. Since the throttle-cable bracket is held in place by the nut holding the carb on its stud, it'll have to go, too. Also note the large stud sticking up out of the center of the carb--we'll deal with it later.

4 The throttle cable is off, and released from the clamp. Now for the springs...

5 Next, loosen the nuts that hold the carb down on its studs; there should be one at each corner of the carb, and one of them will likely be holding the throttle cable bracket.

6 Disconnect the fuel line. In our case, that simply required loosening the hose clamp that held the fuel line to the inline filter. Place a can under it to catch the fuel that’s about to pour out.

7 Disconnect the vacuum lines coming from the carb and lift if off. There should be one vacuum line at the front, and a larger one at the back, which was

8 Put a clean towel in the intake to prevent anything from falling in. Replace the carb studs with the included longer ones, which are required to accommodate the added height of the nitrous plate. The old ones should simply unscrew; if they’re stuck, a pair of Vise-Grips should break them free.

9 Lay the plate in place, with one of the two included gaskets under it. While Zex suggests assembling the hoses later, you may find it helpful to temporarily

10 Begin assembling the nitrous solenoid. There's a filter fitting that goes into the inlet, and one of the 12-inch lengths of braided steel -4 AN line will be screwed into the outlet. AN fittings are measured in increments of 1/16-inch, so this one has an inside diameter of 4/16-inch, or a 1/4-inch.

11 With the inlet and outlet fittings in place, place the solenoid on its mounting bracket. The kit comes with three brackets--one for each solenoid, and one for the throttle switch--made of easily bendable material. These can be oriented in several different directions, thanks to the different hole patterns in the bracket. Mount them to the bottom of the solenoid with the two button-headed screws, using the included hex key.

12 With the solenoid assembled, it's time to hook it up to its fitting. But first, check the instructions to find the correct-sized jet. Since I was adding 100 hp, this required a No. 46 jet. Insert the jet with the conical part pointed away from the plate, and screw on the braided line.

13 The nitrous solenoid in its final position, mounted with an intake bolt. Note that it's tucked up close under the throttle linkage. Wherever you choose to place it, make sure it will clear all moving parts.

14 Assemble the solenoid lines and bracket the same way, using the appropriate fuel jet--in this case a No. 43. The inlet fitting is a barb unit; you'll need to install a tee in the main fuel line to get fuel from it to the solenoid. When we installed the inline fitting (with added pressure gauge, safety switch, and warning-light sending unit), we used a 1/4-inch NPT close union to attach it to the solenoid. This was placed on the other end of the inline fitting and attached the fuel line with a hose clamp.

15 You'll need to lower the carb stud to accommodate the reduced hood clearance. With the air cleaner removed, back off the jam nut and lower the stud until you have plenty of clearance. Place putty on top of the stud and slowly lower the hood. Check the putty for clearance, then do the same with the air cleaner on. Use as much clearance as you can get, remembering that the engine moves around significantly when it's running.

16 The final part to be mounted near the carburetor is the throttle switch. Thanks to an unusual throttle-cable bracket, there was no easy way to do this with the supplied bracket, so we used a flat sheet of aluminum to fabricate a mount that puts the switch directly on the carb beneath the air cleaner.

17 Here's a look at the switch as mounted. Also note the fuel- pressure gauge, which is mounted to an inline fitting connected to the fuel solenoid. This is where we'll affix the low- pressure-light sending unit and kill switch.

18 While the kit comes with wire and the appropriate terminals, you'll have to assemble the wiring. Shown here are a wire stripper and crimper, along with the wire, terminal, heat-shrink tape, and toggle switch. Strip the end of the wire, slide the heat-shrink tube over it, insert the wire into the terminal, and crimp in place. Then slide the tube up over the crimped part of the wire and use a heat gun to seal it up.

19 For the arming circuit, you'll need to locate switched power and run a wire to the supplied 12-volt toggle switch. There's an accessory terminal at the fuseblock that should work. We piggybacked the red wire for the arming circuit onto the yellow power line for our electric wiper-door conversion, as shown.

20 Although it's possible to simply let the switch dangle when in use, it really should be mounted somewhere. In our case, a previous owner had gnawed a 1/2-inch hole in the center stack near the wiper switch, so we used that. This site meets another prime requirement: It's out of the way where we're not likely to activate it accidentally.

21 The wire for the arming switch goes through the firewall and to the relay mounted in the engine compartment. The other wires are for incoming positive power (in this case, from the alternator); a ground wire, which we mounted to one of the threaded bosses on the intake; and outgoing positive power to the solenoids, achieved by joining the two solenoid wires in a single female spade connector.

22 To protect the circuit, there's a 30-amp fuse you'll install in the wire coming from the alternator to the relay. Insert a length of stripped wire in each end of the center-hinged fuse holder, crimp, and heat-shrink. Plug in the mini-fuse, and you're done.

23 Note the two black wires from the top of the solenoid; either can be ground or power. We took one from each solenoid, stripped them, joined them in a ring connector, and used that as a ground mounted to one of the intake bosses. The other two were combined and plugged into the relay as power. Also note the fuel-pressure gauge and its inline fitting. That’s where we mounted the low-pressure sending unit, affixing it to a brass tee between the fitting and gauge. We then drilled and tapped another 1/8-inch NPT hole in the fitting and mounted the kill switch inboard towards the intake, beneath the hard fuel line.

24 Don't forget to change the spark plus prior to running nitrous in your engine. To avoid detonation, you'll need plugs that are at least two steps colder than what you would ordinarily run. These plugs were provided by Zex, and not only are they colder, they have an electrode designed to throw a more efficient spark. Also remember that you must dial back the timing--in this case, by four degrees--again, to reduce the risk of detonation.

25 Low-pressure warning-light kit from Jegs. While intended for oil pressure, it works for fuel pressure as well. I replaced the massive red light with a smaller one ordered from Stafford Vehicle Components in England.

26 Here's the self-grounding 6-psi pressure switch, assembled to the brass tee. For power, we simply unplugged the wire leading from the arming switch and cut off its terminal, then joined the wire going to the pressure-sending unit with it and crimped them in a new female spade connector. While Teflon-thread sealing tape is shown in this photo, liquid thread sealant is the preferred method.

27 We installed our warning light in a 1/2-inch hole in the console.

28 Our safety switch also came from Jegs. Threaded at a standard 1/8-inch pipe thread, the switch screws into an inline fitting and is wired into the arming circuit. With the switch in place, we're ready to start tuning our nitrous system for safe, reliable power.

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